This invention relates to a battery separator and to a method of manufacturing same in which the separator is formed of a plurality of sheets of microporous plastic material adhered together by a strip or a plurality of strips of polyvinylchloride material in a manner suitable to form a sleeve.
Traditionally, wet cell batteries employ at least one pair of opposite polarity planar electrodes, normally referred to as plates, which are closely spaced in a parallel relationship and immersed in a liquid electrolyte to form an electrochemical couple. A great majority of these type batteries employ a plurality of pairs of the opposite polarity plates with the plates being normally arranged in an upstanding face-to-face relation, and with the exact number of pairs in a particular battery depending upon the capacity and/or voltage desired.
To avoid adjacent opposite polarity plates from coming into direct physical contact and thereby causing arcing and/or short circuiting, it is necessary to electrically insulate the adjacent plates from each other. To achieve this insulation, electrically insulative material, usually in the form of sheets similar in size to the electrode plates, and commonly referred to as separators, have been positioned between the opposite polarity plates, with the insulative material being permeable or semipermeable to the liquid electrolyte to sustain the ionic conduction required for the battery action.
In older designs the separators were formed of rubber, wood, and glass while more recent designs have used microporous plastic materials, including polyethylene, vinyl resin, and the like, which have excellent insulating capabilities yet are relatively low in weight and cost. An example of such a plastic separator is disclosed in U.S. Pat. No. 3,696,061, issued Oct. 3, 1972, in the name of Selsor et al and assigned to the same assignee as the present application. The disclosure of this U.S. Pat. No. 3,696,061 is hereby incorporated herein by this reference.
In applications where heavy-duty use and requirements are such that maximum insulating conditions between the positive and negative plates must be provided, such as in the case of industrial batteries, it has been found advantageous to place a sleeve of insulating material upon either the positive or negative plates with the sleeve being formed and folded to dimensions dictated by the plate size. In a typical sleeve configuration, one side is formed by the end portions of the sheet which are overlapped and sealed, so that the sleeve has completely insulating sides to prevent lead dendrites from forming from the negative to the positive plates when the battery is charging and discharging in service.
Although battery separators of a plastic material of the general type disclosed above, and as specifically disclosed in the aforementioned Selsor et al patent have enjoyed widespread commercial success, especially for use in industrial type batteries, such separators are relatively brittle and therefore special means are required to fold the material into the desired sleeve configuration without fracturing or breaking the material. For example, in commonly assigned U.S. patent application Ser. No. 535,980, filed Dec. 23, 1974, there is disclosed a relatively complex and relatively expensive machine for folding such separator material to form sleeves or envelopes without causing fracture or breakage of the material.